Degenerated intervertebral discs are currently treated with fusion cages for arthrodesis, and lower grade degenerated discs are replaced by arthroplasty devices, i.e. total disc replacement (TDR) implants.
Standard surgical procedures for disc replacement with fusion or non fusion devices generally include the following steps, each of which are described in more detail below:                1. Create an approach to the selected disc;        2. Complete or partial removal of the selected disc or disc material (annulus and/or nucleus), e.g., discectomy; and        3. Insert the total disc replacement devices, or intervertebral spacers, or fixation devices such as screws, plates, rod systems, etc.        
An approach through the soft tissue (i.e. skin, muscles, faciae) to a selected intervertebral disc(s) is created such that the soft tissue preferably is kept away from the site and the working area, e.g., by retractors or cannula. The purpose of the approach is to provide a suitable surgical approach and exposure to the appropriate degenerative disc level.
After a suitable approach is achieved the surgeon removes the affected disc material, such as for example the annulus, nucleus or both or portions thereof, with, e.g., curettes, or rongeurs or other instruments. The purpose of this step is to provide adequate discectomy and intervertebral endplate preparation.
After discectomy and endplate preparation, the endplates or vertebrae may be distracted to augment the intersection between the endplates and to create sufficient space for the replacement device. One way to perform this step is to use a distraction instrument.
Next, the surgeon inserts the replacement device in the appropriate position. Proper implant placement is beneficial to ensure optimal results, including segmental motion preservation. After the implant is inserted, the distraction instrument may be removed.
The intervertebral space between vertebral bodies may be approached with different techniques. Several techniques have been described in literature, such as anterior transperitoneal, trans-psoas (true lateral) or posterior approach through median incision. Another technique involves an extraforaminal approach for the insertion of spinal disc implants.
In order to accomplish a less invasive insertion of a TDR implant, suitable methods and instruments are needed to provide the respective support to the surgeon, including a distraction instrument and a mechanically stabilized retraction instrument. Two commonly accepted procedures for stabilization are:
1. use of the table in the operating room (OR) as reference; and
2. “binding” the instrument to the patient.
Considering the nerve root which must be controlled during the surgeon's manipulation, the mechanical link between the instrument and the table might have some short comings such as:                the reference could be lost if the patient is moved on the table, whereas the nerve root is “bound” to the table; and        the surgeon must manipulate outside the conventional sterile area, i.e. underneath the sterile covers on the OR table, which might contaminate the sterile incision area.        
Discussion or citation of a reference herein will not be construed as an admission that such reference is prior art to the present invention.